1. Field of the Invention
The present invention relates to an axial fan unit including two or more coaxially arranged fans.
2. Description of the Related Art
Electronic devices having frames such as personal computers and servers include cooling fans therein. The cooling fans are used for cooling electronic components inside the frames. When density of the electronic components inside the frames increases, concentration of heat generated by the electronic components occurs and lowers performances of the electronic components. In order to prevent this, cooling fans are required to have improved performances.
Among various types of electronic devices, relatively large sized electronic devices such as servers require cooling fans which can achieve both a high static pressure and a large flow rate of air. One example of such cooling fans is an axial fan unit formed by at least two fans connected coaxially with each other. In each of the fans coaxially connected to each other, a plurality of supporting legs for securing an armature to a frame of the axial fan unit and stator vanes attached to the supporting legs are disposed on a downstream side of an impeller in an air flowing direction, i.e., in a direction parallel to or substantially parallel to a center axis of the axial fan unit. That is, the supporting legs and the stator vanes are disposed on an air-outlet side of the impeller in each fan. The supporting legs and the stator vanes extend in a radial direction perpendicular to the center axis.
For cooling fans installed in electronic devices, reducing or minimized noises or operation sounds of the cooling fans are demanded from a viewpoint of improving operation environments where the electronic devices are to be used, for example. However, in the aforementioned exemplary axial fan unit, air sent by each impeller interferes with the supporting legs and stator vanes disposed on the air-outlet side of that impeller, thus increasing noises of the axial fan unit.